Reference Electrodes

So here we have our silver silver chloride reference electrode which is one of the most versatile and most widely used reference electrodes in the field. Now we're gonna say it is typically constructed as a thin tube that is subsequently dipped into solution. So we saw previously this half cell reaction that was closed off by this dotted box. This represents our S. S. C. E. Or silver silver chloride electrode. Uh Reference electrode. We're gonna say here that when it comes to the components of it, we'd say here that this is our wire, lead. And basically here this is where we have our just our silver wire. We have our solution of potassium chloride and silver chloride here this is just our silver chloride paste. And then we have some K. C. L. Solid here as well as some silver chloride solid here this is part of our salt bridge and this is our poorest opening. If the liquid gets too high. It basically comes out here, remember we said that the silver silver chloride electrode is our reference electrode. So its concentration would not change here. We have our indicator electrode. Now, when we when we say that the chloride concentration approaches unity. So that means it comes close to one, we're gonna have a self potential equal to this. That's because when we take into account the reference electrode, which in this case is the silver silver chloride reference electrode, we're gonna say that our standard potential well are nonstandard potential is equal to our standard cell potential minus 10.5916. Divided by the number of electrons transferred times log of chloride ions here. If our chloride ions approach unity, That means that this is gonna become one Log of one is equal to zero. And so all of this drops out and therefore my self potential under nonstandard conditions equals myself potential under standard conditions. Now here we're gonna say the reference electrode is based on the redox couple between silver chloride and silver ion. So here we have the reaction. And what we're gonna say here, what happens is an electron is absorbed by this solid chlorine is the one to accept it and becomes chloride ion. Now here the activity of the chloride ion determines the potential of the electrode. So remember your activity which is a takes into account the activity coefficient as well as the concentration of the ion. In order to figure out the activity. And again remember as it approaches one or unity, we're gonna have some potential other nonstandard conditions equals some potential. Under standard conditions were going to say here when dealing with our saturated chloride chloride solution, we have to keep in mind how are concentrations can affect many things for our solution. So we're gonna say here when it's saturated We had a voltage or .197V. And when it's dipped into a concentration that's greater than that, it increases 2.205V. So like other reference electrodes concentrations can be manipulated um in order to increase or decrease our overall voltage. Here we say that this reference electrode. So this would be potential of our reference electrode. And then over here we deal with the potential of our indicator electrode. So here would be silver solid. Here we have a phase boundary and then we have silver chloride, solid potassium chloride, Aquarius, and then we have the activity of chlorine of chloride ion depending on what it is. So remember there are different types of reference electrodes. This just happens to be one of them here. It may not be the most widely used but it is one of the best versions to use. The hardest of the reference electrodes will talk about which deals with she the standard hydrogen electrode. That one is much more difficult to use because of its implementation setup and cost in running it.

So here we're dealing with a caramel reference electrode. We're gonna say the caramel reference electrode is based on the following redox couple reaction between mercury one chloride and mercury itself. So here we have mercury one chloride solid, It absorbs two moles of electrons to give us two moles of mercury liquid plus two moles of chloride ion. Here we have our typical reference caramel reference electrode. It's usually abbreviated as S. C. E. Now in terms of the components we can say here that it starts off with a wire lead and it leads down to this portion which is our platinum wire. This is just our inert electrode. We're gonna say here we have this is just a hole to allow drainage. And in this compartment here is where we actually have the mercury liquid and if it gets too high the mercury liquid will drain outside of this whole in this compartment here we have our reaction going on. We have our mercury, we have mercury one chloride and we have potassium chloride. Also involved the potassium chloride can help release some chloride ions here and on the bottom here we just have some basically some glass wall and an opening in here we have our saturated solution of K. C. L. Here we have this is our K. C. L. Solid and this is just our porous plug which forms part of the salt bridge. Now we're gonna say that this is the most common type of reference electrode that we can use basically. It's just a slurry of the mercury and mercury one chloride with the saturated K. C. L. In there. And we're going to say here that there are a few things about this particular reference electoral we can mention. So when we're talking about it's nerds equation we're gonna say that it's non standard cell potential equals the standard cell potential of its reduction reaction -15916V, divided by the number of electrons transferred. Here. We have the log of the concentration of chloride ions here we just put a for activity. Remember your activity can equal your activity coefficient times the concentration of the particular ion. If your activity coefficient reaches unity then you can just substitute in pull right eye on here. Okay, so when your activity reaches one you can say that represents concentration of chloride ion here it's squared because in the original equation up above We have a two here, Mercury is not included and Mercury one core is not included because their liquids and solids respectively. We ignore liquids and solids within our equilibrium expressions here. This is our standard cell potential for that half reaction. Now we're gonna say from the equation it determined that the potential of the electrode is based on the activity of the chloride ion because this is really what's changing that can affect my overall cell potential. We're gonna say the concentration of chloride ions is determined by the suitability of K. C. L. So the more soluble K. C. L. Is the more chloride ions you can release which will have an impact here on this. So the larger that is, the larger this overall value will be, which will subtract from this And bring down your overall cell potential make you less spontaneous. So the potential of .268 is when the activity of chloride ion approaches unity so reaches one because when we have log of one for this that equals zero. So all of this would drop out. Now when the concentration of K C. L. Is varied. That can have a direct impact on my voltage. When it's 0.100 moller, the voltage would be 0.336 volts. But if I increase it then my voltage decreases. Because remember we said that the larger this value is, the bigger this overall will be. And the mortal subtract from this standard cell potential here. Now we're going to say here that the potential can also be affected by temperature. So we're gonna say a 25°C, it is approximately .2444V. And at 35°C it's .2376V. Okay, so notice here that we have basically dropping of our voltage because here temperatures affecting the basic concentration which will affect the overall cell potential. And when it comes to the cell notation for this half reaction or this reference electrode, we're going to say here, it's equal to the mercury as a liquid. And then here we have our phase boundary and here we have mercury, one chloride solid times K C L. Saturated and then we have our physical boundary. So here this would be the reference electrode compartment for my sanitation. Remember here we'd have the rest, we could talk about our indicator electrode over here, whatever we're comparing it to. So remember, the S. C. E. Electrode is basically the best out of all of them in terms of use and preparation and cost. But we have to keep in mind that things such as temperature as well as the concentration of our potassium chloride, do have a big impact in the overall cell potential.